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1 INTRODUCTION ' Former Exxon Retail Site (RS) 7-0137 is an active service station located at 1605 South El Dorado Street in Stockton, California There is one 20,000-gallon double-walled fiberglass underground storage tank at the site divided into compartments that contain 60 and 40 percent of the total volume ' capacity A soil vapor extraction system was operated at the site from approximately November 1995 until April 1998 ' A closure request report documenting the results of the recently drilled confirmation borings at the site was submitted to San Joaquin County Public Health Services in November 2000 2 GROUNDWATER MONITORING On 4 December 2000, wells MW1-MW7, VEW1, and VEW2 (Figure 1) were gauged for depth to ' water and for liquid-phase hydrocarbons (LPH) with an optical interface probe Groundwater samples were collected from wells MW1-MW7 and VEW2, and the samples were analyzed for Total Petroleum Hydrocarbons as gasoline (TPH-g), for benzene, toluene, ethylbenzene, and total xylenes ' (BTEX), for the oxygenates methyl t-butyl ether(MTBE), diisopropyl ether (DIPE), t-butyl alcohol (TBA), tert-amyl methyl ether (TAME), tert-butyl ethyl ether (ETBE), and the additives 1,2- dibromoethane(EDB) and 1,2-dichloroethane (1,2-DCA), and for total dissolved lead Well VEW1 was not sampled because it was dry On 28 December 2000, well MWl was resampled and analyzed for TPH-g and BTEX ' The depth-to-water measurements and calculated groundwater elevations are presented in Table 1, along with historical data, and current groundwater elevations are shown in Figure 1 The ' groundwater flow direction on 4 December was to the southeast, with a gradient of approximately 0 001 to 0 003 LPH was not observed in any of the wells ' After the depths to water were measured, the wells were purged Field parameters of pH, temperature, and electrical conductance of the purged water were measured for approximately every well casing volume during purging Copies of the field documents are included as Appendix A When the field parameters were stable (Iess than a 10 percent change from the previous reading for temperature and electrical conductance and not more than 0 1 pH units) and approximately 3 casing volumes were removed from each well, purging was stopped and samples were collected using I factory-cleaned disposable bailers The samples were poured into 40-m1 glass VOA vials and stored in an ice-filled cooler All samples were handled and transported under chain of custody The samples were submitted to SPL, Inc in Houston, Texas, and analyzed for TPH-g by Cal EPA- modified EPA Method 8015, for BTEX by EPA Method 8021B, for MTBE, DIPE, TBA, TAME, ETBE, EDB, and 1,2-DCA by EPA Method 8260B, and for total dissolved lead by EPA Method ' 6010B The results are presented in boldface type, along with previous analytical data, in Table 1, and the petroleum hydrocarbon and MTBE results are shown in Figure 1 The laboratory analytical report and chain-of-custody documentation are included in Appendix B I I IF%PmJ0c1s4701371M=c6WpVQI200\Tr doc 1